The activated sludge process has been used for many years for the treatment of waste water. This process involves the treatment of waste water through the use of suspended biological solids whose activity and quantity is controlled by the addition of oxygen. The aerobic bacteria feeds and grows on the material in the waste water which can be oxidized.
The effluent sewage or waste water is introduced into an aeration tank along with activated sludge. The activated sludge is recycled from final sedimentation tanks. The aeration tank aerates and mixes the waste water and the activated sludge sufficiently to supply the oxygen required by the bacteria in the sludge.
The mixture of waste water and activated sludge, called "mixed liquor", then flows into a settling tank. In the settling tank, the activated sludge solids are separated from the clean, treated water. The activated sludge solids are then returned to the aeration tank to provide the activated sludge for new waste water. In some cases, a sludge reaeration tank is used to aerate the return sludge, but before the sludge is returned to the aeration tank.
U.S. Pat. No. 3,047,492 to Gambrel discloses a sewage process which incorporates an aerobic digester which feeds back into an aeration tank. The patent teaches that, of the sludge removed from the settling tank into the sludge hopper, about 12% should be moved to the aerobic digester and the remaining 88% directed back to the aeration tanks. The patent suggests the aerobic digester operate 14-15 days. However, this length of time is impractical in application because a continuous cycle would require a large number of separate aerobic digesters in order to provide sufficiently aged sludge to maintain the process.
A need continues to exist for more efficient and effective waste water treatment techniques. In processes today, a large quantity of sludge results from the process which must be disposed of. Significant funds are expended by municipalities in disposing of this sludge through the methods approved for the disposal, such as landfill and the like. A process which reduces the resultant quantity of sludge would be of great benefit in reducing the cost of this disposal.